In countries having languages comprising ideographical characters such as China, Japan, Taiwan, paging systems which can transmit, receive and display the ideographical characters are required. Such paging systems are well known: however, several problems have arisen in the development of these ideographical paging systems.
Typically a ideographical paging system comprises a character entry device, a terminal for control and coding functions and display pagers. Each one of a predetermined selection of characters of the language has an associated code, comprising one or more bytes, according to an industrial coding standard. A display pager on receiving a signal having a number of coded bytes decodes the signal according to the industrial code used, reads the corresponding characters from its character generating memory and displays the characters. However, the standard codes used to code the characters vary from one country to another. For example, the standard code in Taiwan is different to the standard code in China. Also, in some cases, there are multiple coding standards within the same country. Therefore, for each of the coding standards different pager models in the paging system are required to be used, even when the same character set has been coded. This makes the ideographical paging system increasingly expensive.
The Japan Industrial Standard (JIS), Peoples Republic of China (PRC), and Taiwan industrial coding standards have been developed to cover a particularly large number of characters. However, in order to code each one of these characters approximately 7000 words are needed which require two-mega-bits (2M bits) of Read Only Memory (ROM) for formatting. As a result excessive memory space is needed to incorporate all these characters into the character generating ROM of the pager.
Another problem associated with an ideographical paging system arises due to the incompatibility of the character sets which can be entered into the entry device, processed in the terminal and displayed in the display pager: this is a direct result of the memory capacity limitation of the terminal and character generating ROM of the pager. Since it is not practical to incorporate all the characters of the language into the system, especially into the memory of the character generating ROM, only a selection of characters are incorporated into the system. The number of characters incorporated depends on the memory capacity, therefore the selection can vary between the entry device with a larger capacity, the terminal and the character generating ROM.
Thus, a problem occurs when a rarely used character is entered via the entry device into the system and the entered character is not one of the predetermined selection of characters stored in the character generating ROM of the pager (such a character will be referred to as an `illegal` character hereafter). When the pager receives an `illegal` character, irrespective of whether the following characters are `illegal` or not, the data decoding is interrupted and no further characters will be displayed. Since the same result occurs when the pager or the system malfunctions, the user of the pager has no information as to why the displayed message is incomplete.
Thus, it is an object of the present invention to provide an improved ideographical signalling system wherein the above problems are overcome.